Kefining benzol light oil for



A. L. TANNEHILL Filed April 9, 1936 WKN h.

March 7, 1939.

' REFININC- BENZOL LIGHT OIL FOR MOTOR FUEL l il Patented Mar. 7, 1939STAT ES PAT ENT OF REFINING BENZOL LIGHT OIL FOR MOTOR FUEL 4 Claims.

'I'he present invention relates to fuels for internal combustion enginesand-more particularly to the refining of crude benzol light oil, asrecovered from coal gas or coke oven gas, to produce motor fuel.

An object of the invention resides in an improved methodof refiningcrude benzol light oil which will be economical in practice and eicientas to yield of finished product.

A further object of the invention is to provide a method of refiningbenzo-l light oil as recovered from coal gas or coke oven gas which willconserve certain hydrocarbon constituents of the light oil, therebyincreasing the yield of finished product.

A further object is to provide a process of refining benzol light oilWhich Will represent an improvement over the present refining process inthat both color and sulphur content of the motor fuel can be controlledwithout sacrifice of any appreciable amount of unsaturated hydrocarboncontent.

Crude benzol light oil contains constituents which make it unsuitablefor motor fuel without some treatment. These constituents may be classedas acidic compounds, unstable unsaturated compounds, unsaturatedcompounds which are relatively stable, sulphur compounds which may bewashed out by means of sulphuric. acid, a sulphur compound which can notbe washed out by sulphuric acid but which may be largely separated intoa fraction called forerunning's and small amounts of unsaturatedcompounds which produce an objectionable color both in the light oil orin a distillate from the light oil.

The treatment necessary to produce a satisfactory motor fuel from'thelight oil may vary, depending on the nature of the light oil and on thespecification for the finished motor fuel.

The acidic constituents consisting mainly of carbon dioxide, hydrogensulphide, hydrocyanic acid and small amounts of mercaptans arel allobjectionable and should always be removed. Especially objectionable ishydrogen which if present in motor fuel causes the fuel to becomecorrosive toward metals, due to oxidation to elemental sulphur. Acidicconstituents are practically always removed by washing with causticalkali.

Common practice is to remove the unsaturated hydrocarbons, or at leastthe more unstable of them, and the color producing compounds, in orderto improve the color and prevent the formation of gummy constituents inthe fuel by (ci. 19t-38)' these constituents. This isgenerally done bytreatment with sulphuric acid.

Some treatment is generally, although not always, necessary to controlthe sulphur content of thenishd fuel. Sulphur exists in light oil mainlyin two forms, as thiophene and as carbon bisulphide;v Thiophene canv bewashed out by means of strong sulphuric acid While carbon bisulphide canbe removed bydiscarding forerunning's, which isthe 'rst'fraction todistill over when the light oil is distilled. Either or both ofthese'methods kof reducing the sulphur content may be used. Chemicalmethods for removing carbonY bisulphide have recently been proposed butas yet vhave had no extensive application.

The older method of refining light oil, and which is still the methodgenerally used, consists of washing the light oil with strong sulphuricvacid in suflicient amount to remove all of the unsaturated hydrocarbons,color produc- E ing compounds and most of the thiophene. The light oilis then washed with caustic alkali, to remove acidic constituents, anddistilled. If necessary to further reduce the sulphur content,forerunnings'are discarded. This method of reningby means of strongsulphuric acid is inefcient as `to yield of finished product andexpensive because of the large amount of chemicals required.

It is now well known that theunsaturated hydrocarbonsYV are valuablefuel constituents if treated by small amounts of certain substances,known as anti-oxidants or gum inhibitors, and it is therefore highlydesirable to leave the unsaturatedhydrocarbons in the fuel.

More recent methods of refining light oil, o

whichY seekfto conserve the unsaturated hydrocarbons, may employ arestricted acid treatment, to remove only the more unstable of theunsaturated hydrocarbons and the color producing constituents, therebyimproving the color and reducing the tendency to gum formation. A guminhibitor may alsobe used. The process is carried out in a mannersimilar to the one described above except that the sulphuric acid usedis restricted as to strength or quantity so as not to remove theunsaturated hydrocarbons which are relatively stable. Thiophene is not'removed by this method in substantial amount and to control the'sulphurit is necessary to discard forerunnings.

Sometimes the'light oil or a fraction of the light oilmay be merelywashed with caustic alkali, to remove acidic constituents, followed by adistillation and the 'addition of an inhibitor. Sulphur content may becontrolled by discarding forerunnings but color is not controlled byYthis y method.

All of the refining methods heretofore Apracticed which aim to conservethe unsaturated hydrocarbons have the disadvantage that thiophenesulphur cannot be removed, the acid treatment, if any, beinginsufficient to remove thiophene. Forerunnings are generally discardedwhen necessary to reduce the sulphur content.

Actual tests have proven that most of the unsaturated hydrocarbons arefound in the forerunnings if the light oil is distilled before theseconstituents are removed. Therefore, since acid treatment drastic enoughto remove thiophene also removes the unsaturated hydrocarbons, and sincemost of the unsaturated hydrocarbons are found in the forerunnings ofthe untreated light oil, prior methods fail to conserve the unsaturatedhydrocarbons to the full extent if the sulphur content is to becontrolled. Furthermore, if

- either sulphur or coloris to be controlled by methods practicedheretofore, unsaturated hydrocarbons must be sacrificed. Y

The present invention furnishes a method whereby the sulphur content ofthe fuel can be reduced by removing thiophene and without destroying asubstantial amount of the unsaturated hydrocarbons.` This is a greatadvantage. In many cases it will offer sufcient control of the sulphurto obviate the necessity for removing carbon bisulphide and'in othercases the amount of carbon bisulphide which'must be removed will bereduced. Furthermore, even though chemical methods for removing carbonbisulphide, now being proposed, and inspired by a desire to conserve theunsaturated hydrocarbons, should prove successful, there still remains agreat advantage in the present method of removing thiophene, as oftenthe removal of carbon bisulphide alone will not give suiiicientreduction in the sulphur content. The process of this invention can beemployed in conjunction with chemical methods for removing carbonbisulphide. Y

The invention also furnishes a method for controlling the color of themotor fuel without loss of a substantial amount of the unsaturatedhydrocarbon content.

The method of this invention also provides an improved method ofremoving acidic constituents, which saves most of the chemicals requiredfor this purpose by former methods.

A still further advantage of the new process of refining light oil isthat where only a portion of the light oil is converted to motor fuel,the remainder being worked up into pure aromatic hydrocarbons, such aspure benzol, pure toluol etc., the rening is accomplished with the useof a greatly reduced quantity of strong sulphuric acid.

By the process of the invention the forerunnings are rst separated fromthe light oil by distillation. The forerunnings, containing most of theunsaturated hydrocarbons and carbon bisulphide, are treated to removeacidic compounds and after adding an inhibitor may become a finishedproduct. The color of the forerunnings is controlled by aging the lightoil for a suitable length of time before distillation. Actual tests haveproven that by aging the light oil for a suitable length of time a waterwhite distillate is obtained. The time of aging may vary from a fewhours to two days or even more. The distillation is preferably conductedin a continuous manner, as by so doing the separation of theforerunnings is more easily and cheaply accomplished and small auxiliaryapparatus can be used. A further and more important advantage ofcontinnous distillation is that by this process the distillate is easilykept out of contact with air until the acidic gases are removed. Contactwith air for any extended time in the presence of hydrogen sulphide willcause the distillate to become corrosive. Batch distillation can,however, be managed so as to avoid harmful oxidation by treating thedistillate continuously, as it comes from the still, for the removal ofacidic constituents. A column still for the distillation iscontemplated.

By the process of the invention, two alternative methodsY for removingacidic compounds from the forerunnings have been provided. I have foundthat by condensing the vapors at the top of the column, returning thecondensate to the top of the column and withdrawing the condensate a fewrings below the top, the acidic gases are mostly expelled as bent gasesand the con-- densate may easily be washed free of the remaining acidcompounds with a very small quantity of caustic alkali. An alternativemethod to the caustic alkali washing is to pass the forerunnings throughan auxiliary column having a boiler at the bottom and a condenser at thetop. The acidic gases are entirely expelled as vent gases and theproduct is withdrawn from the boiler, cooled and an inhibitor added.

I-Ieretofore the acidic compounds have been removed solely by washingwith caustic alkali, which however consumes a considerable amount ofreagent. An advantage of the present method is therefore a saving incaustic alkali requirements.

The inhibitor treated forerunings containing most of the unsaturatedhydrocarbons of the light oil, may be a satisfactory motor fuelproviding the sulphur content is not too high. It will generally happen,however, that the sulphur content will not be low enough, in which casethe forerunnings are blended with a fraction of the light oil which islow in sulphur. This is best prepared by rening the residual light oilfrom the forerunnings distillation by means of strong sulphuric acid,used in sumcient quantity to remove a major portion of the thiophene.This part of the process therefore consists in blending a portion of thelight oil which has been rened by means of strong sulphuric acid with aportion or'fraction which has not been so refined. An inhibitor, whichmust be added to prevent gumming, may be added either to theforerunnings or to the acid rened portion before blending or to theblend, the order of the blending being immaterial. It is generally best,however, to add the inhibitor to the portion which has not been renedwith strong acid since this portion is unstable and must be treated withinhibitor very soon after it is made. Low sulphur benzol is blended withthe forerunnings fraction in such proportion as is desired or as isrequired to meet the sulphur content requirements for the motor fuel. Incase the sulphur content of the finished fuel can not be sufficientlyreduced by blending, it may be desirable to treat the forerunnings bychemical methods for the removal of carbon bisulphide. In this case itwill be so treated before adding an inhibitor. The reiining of theresidual light oil is accomplished with very little acid, since itcontains very little unsaturated hydrocarbons.

Thus, in accordance with the process of the invention, an improvedmethod is provided for rening benzol light oil for motor'fuel whichaffords-means of controlling the color and sulphur content of thefinished motor fuel and at the same time conserves a major portion ofthe unsaturated hydrocarbon content; also, an improved method isprovided for removing acidic compounds from the crude benzol light oil.

The drawing illustrates diagrammatically one preferred arrangement ofapparatus for refining crude benzol light oil according to theinvention.

Numeral I indicates a receiving and storage tank for crude benzol lightoil. The invention controls the color of the finished product by agingthe light oil a suflicient length of time before distillation. The timeof aging may vary from a few hours to two days or even more, dependingon the color required, and is governed by the Volume maintained in thetank. The oil is drawn by pump Il from said storage tank and deliveredthrough pipe l2 to the continuous column still I3. From this stillconsiderable amounts of acidic gases such as hydrogen sulphide, carbondioxide and hydrocyanic acid are removed, being expelled from a vent atthe top of the still as at lli. The light oil is continuously distilledand the forerunnings are Withdrawn from the still near the top. Thestill may comprise a column of fifteen to thirty plates. At the top thecolumn is provided with a condenser p of a size to condense practicallyall the hydrocarbon vapors and return them to the top of the column. Theliquid forerunnings are continuously Withdrawn from about the fourthplate from the top. The oil passes through boiler l5 thereof through thecooler l@ and is eventually delivered to tank l'l. From tank l1 the oilis drawn through pipe I8 by the pump i9 and is forced through pipe 2lito an agitator 2l Where the oil is Washed with strong sulphuric acid andneutralized. The oil is then charged into a iinishing still 22 having aboiler 23. From the still the refined fractions desired for use as motorfuel are draWn oii and delivered through pipe 2li to tank 25. Said tank25 therefore contains an acid Washed distillate and has connectionthrough pipe 26 with the blending tank 2l. Interposed in said pipe is apump 28 for Withdrawing the contents of tank 25 and delivering the sameto the blending tank.

Referring again to the continuous column still i3 the forerunnings areWithdrawn from the top of said still by pipe Sil Which delivers saidforerunnings to a cooler 3l having connection through pipe 32 with thecaustic Washer 33. Said washer 33 comprises a vessel lled with packingmaterial such as broken brick of about one-half inch in size andcontaining caustic solution of about twenty-five per cent strength. Thecaustic alkali solution removes the remaining acidic gases andmercaptans and the product obtained passes the corrosion and doctortest. The forerunnings are withdrawn from the Washer 33 by pipe 3G anddelivered to tank 35 forming a receiver for the forerunnings Where aninhibitor is added thereto. The addition of an inhibiting substance,which may comprise cresol or benzol-amino-phenol prevents the formationof gummy substances in the product. The receiving tank for theforerunnings is connected by pipe Sii with the blending tank 2i, thecontents being Withdrawn from the receiving tank by pump 3l. Thus in theblending tank the distillate from the residue oil which has been refinedby means of strong sulphuric acid is mixed in the proper proportionsWith the forerunnings which have not-been refined by sulphuric acid toform the motor fuel.

As an alternative to the caustic alkali Washing of the forerunnings itis possible to continuously distill the forerunnings in an auxiliarycolumn, taking-the finished product from thevbottom cf the column. Theapparatus for continuously distilling the forerunnings would thereforeeliminate the soda washer.

In accordance with the process of the invention the objectionablecompounds, namely, hydrogen sulphide, carbon dioxide and hydrocyanicacid, all of Which may be termed acidic gases, are removed bydistillation at the continuous column still I3 Without the loss ofappreciable amounts of hydrocarbons. Heretofore these objectionablecompounds have been removed by Washing the light oil With caustic sodasolution, Which however, consumes a considerable amount of caustic soda.An advantage of the present method is therefore a saving in caustic sodasince the acidic gases are largely removed as vent gases. Therefore theforerunnings may be Washed free of the remaining objectionable compoundsincluding mercaptans, using only a very small quantity of caustic soda.

rIhe strong-acid refined fractions removed from the still 23, which areof loW sulphur content, are blended in tank 21 With the inhibitortreated forerunnings fractions in such proportion as is desired or as isrequired to give a finished motor fuel of satisfactory sulphur content.Accordingly, the present process conserves the major portion of theunsaturated hydrocarbons and at the same time provides a means ofcontrolling the color and sulphur content of the product. The processalso greatly reduces the amount of chemicals required for refining lightoil.

What is claimed is:

1. The method of producing motor fuel from benzol light oil, whichcomprises distilling forerunnings from said light oil in such manner asto expel the bulk of the acidic gases as vent gases, Washing saidforerunnings with caustic alkali to further remove objectionablecompounds, Washing the residue oil with sulphuric acid to remove sulphurcompounds, distilling said acid Washed residue oil, blending thedistillate with said Washed forerunnings, and adding an inhibitor.

2. The process of refining benzol light oil for motor fuel, whichcomprises aging said light oil for a period ranging from several hoursto several days depending on the volume of oil and the color required,distilling the forerunnings from said light oil in such manner as toexpel the bulk of the acidic gases as vent gases, washing saidforerunnings with caustic alkali to further remove objectionablecompounds, washing the residue oil with sulphuric acid to remove sulphurcompounds, distilling said acid Washed residue oil, blending thedistillate With said Washed forerunnings and adding an inhibitor.

3. The process of refining benzol light oil for motor fuel, whichcomprises continuously distilling forerunnings from said light oil insuch a manner as to expel the bulk of the acidic gases as vent gases,Washing said forerunnings With a caustic alkali solution ofapproximately 25 per cent strength to remove the remaining objectionableacidic compounds, adding an inhibitor thereto to prevent gumming,Washing the residue oil With strong sulphuric acid to remove sulphurcompounds, distilling said acid Washed residue oil and blending theWashed forerunnings with said last mentioned distillate.

4. The process of refining benzol light oil from motor fuel, whichconsists in continuously distilling said light oil in a column still,condensing substantially all of the hydrocarbon vapors at the top of thecolumn while Venting the acidic gases, returning the condensate to4 thetop of the column, withdrawing the condensate from the column at a pointintermediate between the light oil inlet and the condenser, washing thecondensate so withdrawn with caustic alkali to remove the remainingobjectionable acidic compounds, washing the residue oil with sulphuricacid to remove sulphur compounds, blending said condensate with adistillate of said acid washed residue oil, and adding thereto a guminhibitor.

ARTHUR L. TANNEHILL.

